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From:   David Vernet <void@manifault.com>
To:     linux-kernel@vger.kernel.org
Cc:     peterz@infradead.org, mingo@redhat.com, juri.lelli@redhat.com,
        vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
        rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
        bristot@redhat.com, vschneid@redhat.com, tj@kernel.org,
        roman.gushchin@linux.dev, gautham.shenoy@amd.com,
        kprateek.nayak@amd.com, aaron.lu@intel.com,
        wuyun.abel@bytedance.com, kernel-team@meta.com
Subject: [PATCH v3 1/7] sched: Expose move_queued_task() from core.c
Date:   Wed,  9 Aug 2023 17:12:12 -0500
Message-ID: <20230809221218.163894-2-void@manifault.com>
In-Reply-To: <20230809221218.163894-1-void@manifault.com>
References: <20230809221218.163894-1-void@manifault.com>
MIME-Version: 1.0
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The migrate_task_to() function exposed from kernel/sched/core.c migrates
the current task, which is silently assumed to also be its first
argument, to the specified CPU. The function uses stop_one_cpu() to
migrate the task to the target CPU, which won't work if @p is not the
current task as the stop_one_cpu() callback isn't invoked on remote
CPUs.

While this operation is useful for task_numa_migrate() in fair.c, it
would be useful if move_queued_task() in core.c was given external
linkage, as it actually can be used to migrate any task to a CPU.

A follow-on patch will call move_queued_task() from fair.c when
migrating a task in a shared runqueue to a remote CPU.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: David Vernet <void@manifault.com>
---
 kernel/sched/core.c  | 4 ++--
 kernel/sched/sched.h | 3 +++
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 614271a75525..394e216b9d37 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2519,8 +2519,8 @@ static inline bool is_cpu_allowed(struct task_struct *p, int cpu)
  *
  * Returns (locked) new rq. Old rq's lock is released.
  */
-static struct rq *move_queued_task(struct rq *rq, struct rq_flags *rf,
-				   struct task_struct *p, int new_cpu)
+struct rq *move_queued_task(struct rq *rq, struct rq_flags *rf,
+			    struct task_struct *p, int new_cpu)
 {
 	lockdep_assert_rq_held(rq);
 
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 19af1766df2d..69b100267fd0 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1763,6 +1763,9 @@ init_numa_balancing(unsigned long clone_flags, struct task_struct *p)
 
 #ifdef CONFIG_SMP
 
+
+extern struct rq *move_queued_task(struct rq *rq, struct rq_flags *rf,
+				   struct task_struct *p, int new_cpu);
 static inline void
 queue_balance_callback(struct rq *rq,
 		       struct balance_callback *head,
-- 
2.41.0